So you recently bought a 3d printer or are considering purchasing one. If you’re like most people you probably laughed at the $20-$200K price tag for a professional printer, but instead opted for some decent looking $500 printer. And if you’re anything like me, after the first few hundred magical hours of printing you started to see flaws in your prints; layers don’t seem to be bonding properly, prints keep peeling off the bed and warping, the extruder is putting out too much or too little material, dimensions don’t match that of your .stl file, etc… You almost have to keep a constant eye on the printer for the whole 5 hours it takes to print your Yoda bust.
Well in this series I’m going to offer some tips that I’ve learned to dramatically improve the quality of your 3d prints using Fused Filament Fabrication (FFF) technology. Since I have been working exclusively in ABS and it is one of the more difficult materials, these tips will mainly just apply to printing in ABS plastic.
There are 6 key areas you need to focus on that will greatly impact the quality of your prints (I am likely to edit or change these, just fyi):
- The print bed
- Calibrating the x, y, and z axes and the extruder flow
- The extruder drive mechanism
- Print speed
- Mechanical backlash (typically in the x and y axes)
- Cooling and heating the print
Here I am just going to focus on the print bed.
The Print Bed
The most critical component that will cause you the most grief is the printing bed. I am certain that over half of my initial misprints were due to issues with the print bed. The number one problem is that parts larger than about 3-4 cm tend to warp and lose adhesion as the part cools. The warping happens because as the part cools, it shrinks. Since the print is stuck to the print bed the upper part of the object shrinks causing the corners to lift up off the print bed. It can also take incredible force to keep the print adhered to the bed. This warping effect will ruin a lot of prints or at best deform the print so it is ugly and/or not dimensionally accurate. Shrinkage is something that cannot be escaped, but its effects can be minimized.
The problem of warping can and should be attacked from two directions:
- increase adhesion to the print bed
- reduce the warping effect due to shrinkage
For printing in ABS or other difficult plastics, a heated bed is a must since it greatly helps in both areas.
Increase Adhesion to the Print Bed
There are two conflicting objectives when considering how well objects should stick to the print bed: a) objects should have maximum adhesion while printing, and b) objects should have minimum adhesion when done printing to make removal easier. You can actually achieve both objectives, but given the choice I personally prefer to err on the side of more adhesion because I cannot stand wasting time and material on failed prints.
So how can you improve adhesion to the print bed? The best solution I have seen and which I use is as follows:
- install glass or ceramic/stone tile print bed (must be very flat)
- liberally apply Aqua Net Super Hold hairspray (no Kapton tape needed)
- make sure bed is perfectly level
- make sure bed is at correct height so that there is no gap between each extruded line and the first layer height is as close as possible to the actual height specified in the slicing software
- heat print bed to about 105 °C before printing
- print the first layer very slow
- let bed cool after print is finished, which will let you take the part off with moderate ease
Most problems of warping off the print bed are due to a bed that is not leveled or is not flat. When the extruder nozzle gets too far away from the print bed the filament will not stick to the bed or not stick well enough. The reason it doesn’t stick is because the amount of upward force the print can resist is proportional to the amount of surface contact between the print and the print bed. In order to achieve maximum adhesion there should be no gap between each extruded line when you look at the bottom of your print.
An unleveled bed is fairly easy to fix by running through the steps to level your bed. A bed that is not flat is a little harder to fix. You can try to accommodate for the problem by printing a thick first layer or printing a raft which will increase surface contact, but a thick first layer will still have gaps and a raft can make it harder to get great prints. The best solution I have found is to get a sheet of heat resistant glass such as borosilicate (can be expensive) or a very flat ceramic or stone tile cut to the size of the bed and then install in on top of the heated print bed. The problem with metal print beds is that metal warps a decent amount when heated. Ceramic, stone, and glass don’t warp any significant amount. The sheet should be well secured to the bed (binder clips work pretty well).
A heated bed will actually provide better adhesion as well as help reduce warping from the cooling. A heated bed by itself is not enough though. People have suggested a number of surface treatments to increase adhesion, including: coating the bed with blue painters tape, installing Kapton tape on the print bed, cleaning the print bed with acetone, or applying an ABS/acetone slurry to the bed. However, the option I have found to provide the most adhesion is spraying the bed with Aqua Net Super Hold hairspray (I’ve tried another brand and Aqua Net is definitely superior). This method is a great choice because it’s easy to apply, it’s cheap, and it sticks well to any surface (kapton tape, glass, etc…). The best part about using Aqua Net hairspray though is that it holds parts very well when heated, and parts typically come right off once it cools down (I’ve had a total of one print that gave me a little trouble after cooling). Hairspray is best when used directly on a glass or ceramic bed since you never have to worry about replacing that expensive Kapton tape. You can also use a razor to help remove parts if necessary.
Aside from these tips, another simple step you should take that will really help is to reduce the first layer speed if your slicer will allow it; I like to print the first layer at around 10 mm/s. This improves adhesion and keeps the filament from being pulled off the print bed. You can also print with a brim or a raft to increase the surface area contacting the print bed.
Reduce the Warping Forces Due to Shrinkage
This is where a heated print bed is necessary for printing in ABS or other plastics prone to shrinkage. The percentage that the plastic shrinks is proportional to the change in temperature. A heated print bed is designed to keep the object at an elevated temperature while printing, reducing the amount of shrinkage.
Ideally the whole print should be kept at around 105 °C for ABS plastic, which is the glass transition temperature. This is the ideal temperature because you want the temperature as high as possible without the possibility of the plastic deforming (I think you could have a slightly higher temperature, but I have not been able to try this yet). Professional FFF printers will heat up the whole print chamber to get the same temperature over the whole print; this is certainly a great improvement you can make to your printer, but requires some work. A simple step which will help is to simply enclose the print chamber to try to contain some of the heat from the print bed.
On the other side of the temperature equation, you can try printing at a lower temperature. This will reduce the temperature difference and therefore shrinkage. However, printing at a lower temperature can decrease layer bonding, increase the chance of filament slipping on the extruder drive mechanism, decrease print quality, and increase the chance of a plugged nozzle. I personally keep my temperature at 220-230 °C and don’t usually print below 210 °C.
Having a heated print bed or print chamber are sometimes not enough though. Shrinkage on large prints can create tremendous forces causing the print to warp off the bed. One way to greatly reduce this force for large prints is to not print at 100% solid infill. A good infill that will still provide a good amount of strength is 20-30% infill. Another way to reduce the force is to change the way you design your parts. While 3d printing is more versatile in this area, a lot of the same principles that apply to plastic injection molding for avoiding shrinkage problems apply to 3d printing. You can learn a lot more about designing for plastic injection molding at protolabs.com. Specifically, see the documents regarding “coring out”, “wall thickness: recommended”, and “wall thickness: uniform”.
If you have any tips you use to help with keeping prints on the platform I’d love to hear them in the comments below.